This application relates generally to computer disc drives and more particularly to adaptive data format and head switch sequencing in a drive control system.
Disc drives enable users of modern computer systems to store and retrieve vast amounts of data in a fast and efficient manner. A typical disc drive houses a number of circular, magnetic discs (such as one to ten) which are axially aligned and rotated by a spindle motor at a constant, high speed (such as 10,000 revolutions per minute). As the discs are rotated, an actuator assembly moves an array of read/write heads over the surfaces of the discs to store and retrieve the data from tracks defined on the surfaces of the discs.
A closed loop digital servo control system is typically used to control the position of the heads relative to the tracks. The servo system generates a signal indicative of the position of the heads. In response to the detected position, the servo system outputs current to an actuator motor (such as a voice coil motor, or VCM) utilized to pivot the actuator assembly, and hence the heads, across the disc surfaces. The heads are positioned over a set of substantially circular tracks of data on the data discs. The multiple tracks are axially aligned and form what are known in the industry as cylinders. A common method of addressing into data discs is by using physical cylinder head sector (PCHS) addressing.
It is a continuing trend in the disc drive industry to provide successive generations of disc drive products with ever increasing data storage capacities and data transfer rates. Because the amount of disc surface area available for the recording of data remains substantially constant (or even decreases as disc drive form factors become smaller), substantial advancements in areal recording densities, both in terms of the number of bits that can be recorded on each track as well as the number of tracks on each disc, are continually being made in order to facilitate such increases in data capacity.
Ideally, the read/write heads are perfectly aligned, so that when a head switch is made from one head to another, the head is already in the proper track position. However, during the disc drive assembly process, heads are frequently misaligned. When head misalignment occurs, another seek is required after the head switch to properly position the head with respect to the desired track. As a result, head switch times are increased due to the extra seek needed to position the read/write head. With the increasing track density (TPI), if heads are misaligned by 1%, the resulting difference in track position can be large.
The head switch time (with the additional seek) in the worst case, is greater than the time it would take to perform a track switch operation. A track switch operation involves using the current head to get to the desired track rather than switching heads. When a track switch is faster than a head switch, it would be preferable to use a track switch operation. Within the surface of a disc, head switching can be faster than track switching at different areas of the surface. Thus, it would be desirable to choose dynamically which switching method is utilized depending on where the head is on the surface of the disc. However, current methods of disc drive assembly do not allow for choosing between the two switching methods based on the switching times at different areas on the disc.
Accordingly there is a need for a method of adapting data format and head switching sequence to specific disc drives.
Embodiments of the present invention improve seek times by adapting switching schemes utilized in an individual disc drive. One embodiment employs a method of selecting a switching scheme for each of a number of zones of a data disc, depending on timing characteristics of the specific disc drive and its data disc or discs. As such, the switching scheme that is used for one disc drive of a particular model of disc drives may be different from the switching scheme used for another disc drive even of the same model.